Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$12.25	9.771%	$13.4469	$13.45	$13.45	$13.40
Purchase #2	$124.67	5.868%	$131.9856	$131.99	$132.00	$132.00
Purchase #3	$246.73	11.641%	$275.4518	$275.45	$275.45	$275.50
Purchase #4	$165.40	13.110%	$187.0839	$187.08	$187.10	$187.10
Purchase #5	$100.35	8.719%	$109.0995	$109.10	$109.10	$109.10
Purchase #6	$237.76	3.307%	$245.6227	$245.62	$245.60	$245.60
Purchase #7	$178.93	4.750%	$187.4292	$187.43	$187.45	$187.40
7 purchase totals =	$1,066.09		$1,150.1196	$1,150.12	$1,150.15	$1,150.10